After a numeral, designates the relative heading, from a given point and heading, to another point, as if the given point is at the centre of a clock and the numeral twelve is aligned with the given heading
After a numeral, designates the time when the minute hand of a clock or watch points to twelve (as opposed to a certain number of minutes before or after that time) and the hour hand points to the specified numeral
You use o'clock after numbers from one to twelve to say what time it is. For example, if you say that it is 9 o'clock, you mean that it is nine hours after midnight or nine hours after midday. The trouble began just after ten o'clock last night I went to sleep, and at two o'clock in the morning I woke up. one o'clock/two o'clock etc one of the times when the clock shows the exact hour as a number from 1 to 12 (of the clock)